NUCLEAR POWER PLANT MOCHOVCE
NPP Mochovce consists of four units of WWER 440 reactors, V-213 type, with improved safety. The first unit was commissioned in 1998, as to the unit 2 in 2000 individual phases of power increase commissioning test took place and after completion of all these tests the unit 2 was put into commercial operation. Units 3 and 4 are in construction phase, which was interrupted in 1994. By the end of January 2000 the repair of turbine generator on unit 1 was completed and power rate of this unit was increased from 55% to full power 100% Nnom. During 2000 also part of the safety improvement programme was implemented, which was imposed by UJD. From the beginning of 2000 the power commissioning tests on unit 2 were conducted at power levels 50 to 100 %. The completion of all power commissioning tests on March 3, 2000 followed by a 144-hours trial run which finished on March 19, 2000 was a significant milestone during power commissioning of Unit 2 in 2000. The approval to commercial operation of Unit 2 NPP Mochovce for the period according to the design was issued by UJD´s Decision of October 4, 2000.
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In 2000 UJD assessed proposals of new Limits and Conditions of safety operations for both operating units which were prepared by the utility based on experience from commissioning of units 1 and 2. The implementation of new symptom oriented procedures already during commissioning of unit 2 was a significant step for more effective solution of possible failures by operational personnel. The procedures were agreed by UJD. A separate category of assessment activity was represented by review of documentation of safety measures contained in the Programme of safety improvements for NPP Mochovce, which were realised during the outage of both units in the middle of 2000. During the outage of Unit 2, the relevant part of in-service inspections programme for classified equipment was realised, in the scope corresponding to due cycle of operational inspections. During in-service inspections only non-significant faults having a nature of mechanical damage were found on connecting material and sealing surface of flange joints. Based on results of in-service inspections, the technical conditions of equipment on Unit 1 and 2 can be evaluated as good. An evaluation and positive judgement of the test results of the reactor cooling system in case of seismic event at this NPP was a significant step of demonstration of the high level safety on NPP Mochovce. Assessment activities at NPP Mochovce were focused on unit 2, which was in a power commissioning stage at the beginning of 2000. Activities of UJD focused on evaluation and assessment of safety system tests within the programme of power commissioning of unit 2.
During 2000 the changes of the individual quality assurance programmes and also the programmes of non destructive defectoscopic in-service inspections of classified equipment of units 1 and 2 resulted from the evaluation of stage of pre-operational control were reviewed and assessed. During the start up of unit 1 of NPP Mochovce the event occurred which was classified as INES level 1 - a short-time violation of plant parameters due to human factor, which at the same time meant violation of Limits and Conditions. Moreover this case was not safety significant. The automatic reactor protection system on Unit 1 was actuated 2 times, from that 1 time on low power level. On unit 2 the actuation of automatic reactor protection was recorded 3 times during power commissioning and at three events actuation of the safety actuation systems (SIS) was recorded. Since the completion of the commissioning of unit 2 no actuation of any reactor protection system has occurred, what is also world-wide outstanding result. Total number and the nature of events on units 1 and 2 on NPP Mochovce does not exceed the framework of common operational failures and their causes common for a new equipment. The systems and equipment important to safety had been working reliable during all the year 2000.
Construction works on units 3 and 4 of NPP Mochovce were interrupted. Based on the operator’s requirement UJD reviewed the proposal of the programme of equipment preserving and made an inspection of the state of the equipment during preserving time period.
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Inspection activities of UJD at NPP Mochovce focused on commissioning and plant operation, on meeting limits and conditions of safe operation, observance of operational procedures by operating personnel and on performing periodic tests of equipment according to programmes prepared.
On Units 1 and 2 of NPP Mochovce in 2000 the following inspections were conducted focused on:
- inspection of plant operation
- inspection of fire safety
- inspection of observing the limits and conditions and track records
- periodical checks and inspections of safety related equipment during operation.
Beyond the scope of inspection plan, a lot of special inspections were performed on Units 1 and 2, focusing on:
- physical protection
- nuclear materials
- emergency preparedness
- storage of radioactive waste in the premises of the power plant
- quality assurance system
- quality of issued documentation
- status on NPP components and systems
- preparation and realisation of safety measures during common outages of both reactor units.
Routine inspection on Unit 1 focused on observing regime at the unit control room, using valid documentation, observing limits and conditions, as well as observing operational regulations and procedures. Findings of routine inspections most often represented incompatibilities between operational procedures and the as-built status of the equipment after implementation of safety measures, observing plant process discipline and keeping cleanness in room on Unit 1. The findings were entered into the logbook of regulatory supervision or into a quarter protocol together with the imposed measures and orders of the inspectors to remove the shortcomings found. Based on the shortcomings found UJD imposed to the operator corresponding measures.
At the end of power commissioning of Unit 2 UJD organised a team inspection to cheek readiness to trial operation and also readiness to transition on commercial operation of Unit 2 of NPP Mochovce. The results of team inspection based on documentation submitted after considering state of plant equipment and systems as well as activities of operating personnel showed a good readiness of unit 2 to transition on commercial operation and therefore UJD issued its Decision-making Act on approval to put this unit into operation. Routine inspections on Unit 2 after its transition to trial operation and following to commercial operation focused on observing plant process discipline by operating personnel at main control room and also by shift personnel according to valid documentation for inspection of periodic tests of the safety systems execution in compliance with the approved limits and conditions, further inspection of fulfilment of measures imposed by the UJD´s protocols and decisions and to inspection of limits and conditions.
Findings of these routine inspections consisting most often in violation of plant operation discipline, in keeping of cleanliness in Unit 2 rooms, in incompatibility between operational procedures and actual state of equipment, were solved by the binding orders of inspectors. A permanent attention has been devoting by UJD to checking and inspection of meeting the conditions of UJD ´s decision by which an approval to commercial operation of Unit 2 of NPP Mochovce was issued and by which UJD more precisely specified the conditions for the operation of Unit 1.
Besides planned inspections also three unplanned plant operation related inspections were performed focused on evaluation of the utility procedure in connection with operation events on units 1 and 2. Considering the results of these inspections the obligatory orders to the operator were issued by the inspection team with fixed terms of fulfilment of the orders, which consequently the operator met.
Based on assessment of operational events, the results of evaluation and inspection activities as well as with regards to safety indicators UJD evaluated the operation of units 1 and 2 of NPP Mochovce as safe and reliable.
The number of events on units 1 and 2 of NPP Mochovce:
The total number 57, from it: INES 1lmiiol 1
The number of reactor scrams on units 1 and 2 of NPP Mochovce:
mmmmmUnit 2mmmmmm3 (during commissioning tests)
A summary colective dose for the year 2000 ( values are linked to the double unit): 49,48 man mSv